function sha1_file(str_filename) {
  //  discuss at: http://phpjs.org/functions/sha1_file/
  // original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  //  depends on: file_get_contents
  //  depends on: sha1
  //        test: skip
  //   example 1: sha1_file('http://kevin.vanzonneveld.net/pj_test_supportfile_1.htm');
  //   returns 1: '40bd001563085fc35165329ea1ff5c5ecbdbbeef'

  var buf = this.file_get_contents(str_filename);

  return this.sha1(buf);
}